clang/lib/CodeGen/CGCoroutine.cpp

   1 //===----- CGCoroutine.cpp - Emit LLVM Code for C++ coroutines ------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This contains code dealing with C++ code generation of coroutines.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "CGCleanup.h"
  14 #include "CodeGenFunction.h"
  15 #include "llvm/ADT/ScopeExit.h"
  16 #include "clang/AST/StmtCXX.h"
  17 #include "clang/AST/StmtVisitor.h"
  18
  19 using namespace clang;
  20 using namespace CodeGen;
  21
  22 using llvm::Value;
  23 using llvm::BasicBlock;
  24
  25 namespace {
  26 enum class AwaitKind { Init, Normal, Yield, Final };
  27 static constexpr llvm::StringLiteral AwaitKindStr[] = {"init", "await", "yield",
  28                                                        "final"};
  29 }
  30
  31 struct clang::CodeGen::CGCoroData {
  32   // What is the current await expression kind and how many
  33   // await/yield expressions were encountered so far.
  34   // These are used to generate pretty labels for await expressions in LLVM IR.
  35   AwaitKind CurrentAwaitKind = AwaitKind::Init;
  36   unsigned AwaitNum = 0;
  37   unsigned YieldNum = 0;
  38
  39   // How many co_return statements are in the coroutine. Used to decide whether
  40   // we need to add co_return; equivalent at the end of the user authored body.
  41   unsigned CoreturnCount = 0;
  42
  43   // A branch to this block is emitted when coroutine needs to suspend.
  44   llvm::BasicBlock *SuspendBB = nullptr;
  45
  46   // The promise type's 'unhandled_exception' handler, if it defines one.
  47   Stmt *ExceptionHandler = nullptr;
  48
  49   // A temporary i1 alloca that stores whether 'await_resume' threw an
  50   // exception. If it did, 'true' is stored in this variable, and the coroutine
  51   // body must be skipped. If the promise type does not define an exception
  52   // handler, this is null.
  53   llvm::Value *ResumeEHVar = nullptr;
  54
  55   // Stores the jump destination just before the coroutine memory is freed.
  56   // This is the destination that every suspend point jumps to for the cleanup
  57   // branch.
  58   CodeGenFunction::JumpDest CleanupJD;
  59
  60   // Stores the jump destination just before the final suspend. The co_return
  61   // statements jumps to this point after calling return_xxx promise member.
  62   CodeGenFunction::JumpDest FinalJD;
  63
  64   // Stores the llvm.coro.id emitted in the function so that we can supply it
  65   // as the first argument to coro.begin, coro.alloc and coro.free intrinsics.
  66   // Note: llvm.coro.id returns a token that cannot be directly expressed in a
  67   // builtin.
  68   llvm::CallInst *CoroId = nullptr;
  69
  70   // Stores the llvm.coro.begin emitted in the function so that we can replace
  71   // all coro.frame intrinsics with direct SSA value of coro.begin that returns
  72   // the address of the coroutine frame of the current coroutine.
  73   llvm::CallInst *CoroBegin = nullptr;
  74
  75   // Stores the last emitted coro.free for the deallocate expressions, we use it
  76   // to wrap dealloc code with if(auto mem = coro.free) dealloc(mem).
  77   llvm::CallInst *LastCoroFree = nullptr;
  78
  79   // If coro.id came from the builtin, remember the expression to give better
  80   // diagnostic. If CoroIdExpr is nullptr, the coro.id was created by
  81   // EmitCoroutineBody.
  82   CallExpr const *CoroIdExpr = nullptr;
  83 };
  84
  85 // Defining these here allows to keep CGCoroData private to this file.
  86 clang::CodeGen::CodeGenFunction::CGCoroInfo::CGCoroInfo() {}
  87 CodeGenFunction::CGCoroInfo::~CGCoroInfo() {}
  88
  89 static void createCoroData(CodeGenFunction &CGF,
  90                            CodeGenFunction::CGCoroInfo &CurCoro,
  91                            llvm::CallInst *CoroId,
  92                            CallExpr const *CoroIdExpr = nullptr) {
  93   if (CurCoro.Data) {
  94     if (CurCoro.Data->CoroIdExpr)
  95       CGF.CGM.Error(CoroIdExpr->getBeginLoc(),
  96                     "only one __builtin_coro_id can be used in a function");
  97     else if (CoroIdExpr)
  98       CGF.CGM.Error(CoroIdExpr->getBeginLoc(),
  99                     "__builtin_coro_id shall not be used in a C++ coroutine");
 100     else
 101       llvm_unreachable("EmitCoroutineBodyStatement called twice?");
 102
 103     return;
 104   }
 105
 106   CurCoro.Data = std::unique_ptr<CGCoroData>(new CGCoroData);
 107   CurCoro.Data->CoroId = CoroId;
 108   CurCoro.Data->CoroIdExpr = CoroIdExpr;
 109 }
 110
 111 // Synthesize a pretty name for a suspend point.
 112 static SmallString<32> buildSuspendPrefixStr(CGCoroData &Coro, AwaitKind Kind) {
 113   unsigned No = 0;
 114   switch (Kind) {
 115   case AwaitKind::Init:
 116   case AwaitKind::Final:
 117     break;
 118   case AwaitKind::Normal:
 119     No = ++Coro.AwaitNum;
 120     break;
 121   case AwaitKind::Yield:
 122     No = ++Coro.YieldNum;
 123     break;
 124   }
 125   SmallString<32> Prefix(AwaitKindStr[static_cast<unsigned>(Kind)]);
 126   if (No > 1) {
 127     Twine(No).toVector(Prefix);
 128   }
 129   return Prefix;
 130 }
 131
 132 static bool memberCallExpressionCanThrow(const Expr *E) {
 133   if (const auto *CE = dyn_cast<CXXMemberCallExpr>(E))
 134     if (const auto *Proto =
 135             CE->getMethodDecl()->getType()->getAs<FunctionProtoType>())
 136       if (isNoexceptExceptionSpec(Proto->getExceptionSpecType()) &&
 137           Proto->canThrow() == CT_Cannot)
 138         return false;
 139   return true;
 140 }
 141
 142 // Emit suspend expression which roughly looks like:
 143 //
 144 //   auto && x = CommonExpr();
 145 //   if (!x.await_ready()) {
 146 //      llvm_coro_save();
 147 //      x.await_suspend(...);     (*)
 148 //      llvm_coro_suspend(); (**)
 149 //   }
 150 //   x.await_resume();
 151 //
 152 // where the result of the entire expression is the result of x.await_resume()
 153 //
 154 //   (*) If x.await_suspend return type is bool, it allows to veto a suspend:
 155 //      if (x.await_suspend(...))
 156 //        llvm_coro_suspend();
 157 //
 158 //  (**) llvm_coro_suspend() encodes three possible continuations as
 159 //       a switch instruction:
 160 //
 161 //  %where-to = call i8 @llvm.coro.suspend(...)
 162 //  switch i8 %where-to, label %coro.ret [ ; jump to epilogue to suspend
 163 //    i8 0, label %yield.ready   ; go here when resumed
 164 //    i8 1, label %yield.cleanup ; go here when destroyed
 165 //  ]
 166 //
 167 //  See llvm's docs/Coroutines.rst for more details.
 168 //
 169 namespace {
 170   struct LValueOrRValue {
 171     LValue LV;
 172     RValue RV;
 173   };
 174 }
 175 static LValueOrRValue emitSuspendExpression(CodeGenFunction &CGF, CGCoroData &Coro,
 176                                     CoroutineSuspendExpr const &S,
 177                                     AwaitKind Kind, AggValueSlot aggSlot,
 178                                     bool ignoreResult, bool forLValue) {
 179   auto *E = S.getCommonExpr();
 180
 181   auto Binder =
 182       CodeGenFunction::OpaqueValueMappingData::bind(CGF, S.getOpaqueValue(), E);
 183   auto UnbindOnExit = llvm::make_scope_exit([&] { Binder.unbind(CGF); });
 184
 185   auto Prefix = buildSuspendPrefixStr(Coro, Kind);
 186   BasicBlock *ReadyBlock = CGF.createBasicBlock(Prefix + Twine(".ready"));
 187   BasicBlock *SuspendBlock = CGF.createBasicBlock(Prefix + Twine(".suspend"));
 188   BasicBlock *CleanupBlock = CGF.createBasicBlock(Prefix + Twine(".cleanup"));
 189
 190   // If expression is ready, no need to suspend.
 191   CGF.EmitBranchOnBoolExpr(S.getReadyExpr(), ReadyBlock, SuspendBlock, 0);
 192
 193   // Otherwise, emit suspend logic.
 194   CGF.EmitBlock(SuspendBlock);
 195
 196   auto &Builder = CGF.Builder;
 197   llvm::Function *CoroSave = CGF.CGM.getIntrinsic(llvm::Intrinsic::coro_save);
 198   auto *NullPtr = llvm::ConstantPointerNull::get(CGF.CGM.Int8PtrTy);
 199   auto *SaveCall = Builder.CreateCall(CoroSave, {NullPtr});
 200
 201   auto *SuspendRet = CGF.EmitScalarExpr(S.getSuspendExpr());
 202   if (SuspendRet != nullptr && SuspendRet->getType()->isIntegerTy(1)) {
 203     // Veto suspension if requested by bool returning await_suspend.
 204     BasicBlock *RealSuspendBlock =
 205         CGF.createBasicBlock(Prefix + Twine(".suspend.bool"));
 206     CGF.Builder.CreateCondBr(SuspendRet, RealSuspendBlock, ReadyBlock);
 207     CGF.EmitBlock(RealSuspendBlock);
 208   }
 209
 210   // Emit the suspend point.
 211   const bool IsFinalSuspend = (Kind == AwaitKind::Final);
 212   llvm::Function *CoroSuspend =
 213       CGF.CGM.getIntrinsic(llvm::Intrinsic::coro_suspend);
 214   auto *SuspendResult = Builder.CreateCall(
 215       CoroSuspend, {SaveCall, Builder.getInt1(IsFinalSuspend)});
 216
 217   // Create a switch capturing three possible continuations.
 218   auto *Switch = Builder.CreateSwitch(SuspendResult, Coro.SuspendBB, 2);
 219   Switch->addCase(Builder.getInt8(0), ReadyBlock);
 220   Switch->addCase(Builder.getInt8(1), CleanupBlock);
 221
 222   // Emit cleanup for this suspend point.
 223   CGF.EmitBlock(CleanupBlock);
 224   CGF.EmitBranchThroughCleanup(Coro.CleanupJD);
 225
 226   // Emit await_resume expression.
 227   CGF.EmitBlock(ReadyBlock);
 228
 229   // Exception handling requires additional IR. If the 'await_resume' function
 230   // is marked as 'noexcept', we avoid generating this additional IR.
 231   CXXTryStmt *TryStmt = nullptr;
 232   if (Coro.ExceptionHandler && Kind == AwaitKind::Init &&
 233       memberCallExpressionCanThrow(S.getResumeExpr())) {
 234     Coro.ResumeEHVar =
 235         CGF.CreateTempAlloca(Builder.getInt1Ty(), Prefix + Twine("resume.eh"));
 236     Builder.CreateFlagStore(true, Coro.ResumeEHVar);
 237
 238     auto Loc = S.getResumeExpr()->getExprLoc();
 239     auto *Catch = new (CGF.getContext())
 240         CXXCatchStmt(Loc, /*exDecl=*/nullptr, Coro.ExceptionHandler);
 241     auto *TryBody = CompoundStmt::Create(CGF.getContext(), S.getResumeExpr(),
 242                                          FPOptionsOverride(), Loc, Loc);
 243     TryStmt = CXXTryStmt::Create(CGF.getContext(), Loc, TryBody, Catch);
 244     CGF.EnterCXXTryStmt(*TryStmt);
 245   }
 246
 247   LValueOrRValue Res;
 248   if (forLValue)
 249     Res.LV = CGF.EmitLValue(S.getResumeExpr());
 250   else
 251     Res.RV = CGF.EmitAnyExpr(S.getResumeExpr(), aggSlot, ignoreResult);
 252
 253   if (TryStmt) {
 254     Builder.CreateFlagStore(false, Coro.ResumeEHVar);
 255     CGF.ExitCXXTryStmt(*TryStmt);
 256   }
 257
 258   return Res;
 259 }
 260
 261 RValue CodeGenFunction::EmitCoawaitExpr(const CoawaitExpr &E,
 262                                         AggValueSlot aggSlot,
 263                                         bool ignoreResult) {
 264   return emitSuspendExpression(*this, *CurCoro.Data, E,
 265                                CurCoro.Data->CurrentAwaitKind, aggSlot,
 266                                ignoreResult, /*forLValue*/false).RV;
 267 }
 268 RValue CodeGenFunction::EmitCoyieldExpr(const CoyieldExpr &E,
 269                                         AggValueSlot aggSlot,
 270                                         bool ignoreResult) {
 271   return emitSuspendExpression(*this, *CurCoro.Data, E, AwaitKind::Yield,
 272                                aggSlot, ignoreResult, /*forLValue*/false).RV;
 273 }
 274
 275 void CodeGenFunction::EmitCoreturnStmt(CoreturnStmt const &S) {
 276   ++CurCoro.Data->CoreturnCount;
 277   const Expr *RV = S.getOperand();
 278   if (RV && RV->getType()->isVoidType() && !isa<InitListExpr>(RV)) {
 279     // Make sure to evaluate the non initlist expression of a co_return
 280     // with a void expression for side effects.
 281     RunCleanupsScope cleanupScope(*this);
 282     EmitIgnoredExpr(RV);
 283   }
 284   EmitStmt(S.getPromiseCall());
 285   EmitBranchThroughCleanup(CurCoro.Data->FinalJD);
 286 }
 287
 288
 289 #ifndef NDEBUG
 290 static QualType getCoroutineSuspendExprReturnType(const ASTContext &Ctx,
 291   const CoroutineSuspendExpr *E) {
 292   const auto *RE = E->getResumeExpr();
 293   // Is it possible for RE to be a CXXBindTemporaryExpr wrapping
 294   // a MemberCallExpr?
 295   assert(isa<CallExpr>(RE) && "unexpected suspend expression type");
 296   return cast<CallExpr>(RE)->getCallReturnType(Ctx);
 297 }
 298 #endif
 299
 300 LValue
 301 CodeGenFunction::EmitCoawaitLValue(const CoawaitExpr *E) {
 302   assert(getCoroutineSuspendExprReturnType(getContext(), E)->isReferenceType() &&
 303          "Can't have a scalar return unless the return type is a "
 304          "reference type!");
 305   return emitSuspendExpression(*this, *CurCoro.Data, *E,
 306                                CurCoro.Data->CurrentAwaitKind, AggValueSlot::ignored(),
 307                                /*ignoreResult*/false, /*forLValue*/true).LV;
 308 }
 309
 310 LValue
 311 CodeGenFunction::EmitCoyieldLValue(const CoyieldExpr *E) {
 312   assert(getCoroutineSuspendExprReturnType(getContext(), E)->isReferenceType() &&
 313          "Can't have a scalar return unless the return type is a "
 314          "reference type!");
 315   return emitSuspendExpression(*this, *CurCoro.Data, *E,
 316                                AwaitKind::Yield, AggValueSlot::ignored(),
 317                                /*ignoreResult*/false, /*forLValue*/true).LV;
 318 }
 319
 320 // Hunts for the parameter reference in the parameter copy/move declaration.
 321 namespace {
 322 struct GetParamRef : public StmtVisitor<GetParamRef> {
 323 public:
 324   DeclRefExpr *Expr = nullptr;
 325   GetParamRef() {}
 326   void VisitDeclRefExpr(DeclRefExpr *E) {
 327     assert(Expr == nullptr && "multilple declref in param move");
 328     Expr = E;
 329   }
 330   void VisitStmt(Stmt *S) {
 331     for (auto *C : S->children()) {
 332       if (C)
 333         Visit(C);
 334     }
 335   }
 336 };
 337 }
 338
 339 // This class replaces references to parameters to their copies by changing
 340 // the addresses in CGF.LocalDeclMap and restoring back the original values in
 341 // its destructor.
 342
 343 namespace {
 344   struct ParamReferenceReplacerRAII {
 345     CodeGenFunction::DeclMapTy SavedLocals;
 346     CodeGenFunction::DeclMapTy& LocalDeclMap;
 347
 348     ParamReferenceReplacerRAII(CodeGenFunction::DeclMapTy &LocalDeclMap)
 349         : LocalDeclMap(LocalDeclMap) {}
 350
 351     void addCopy(DeclStmt const *PM) {
 352       // Figure out what param it refers to.
 353
 354       assert(PM->isSingleDecl());
 355       VarDecl const*VD = static_cast<VarDecl const*>(PM->getSingleDecl());
 356       Expr const *InitExpr = VD->getInit();
 357       GetParamRef Visitor;
 358       Visitor.Visit(const_cast<Expr*>(InitExpr));
 359       assert(Visitor.Expr);
 360       DeclRefExpr *DREOrig = Visitor.Expr;
 361       auto *PD = DREOrig->getDecl();
 362
 363       auto it = LocalDeclMap.find(PD);
 364       assert(it != LocalDeclMap.end() && "parameter is not found");
 365       SavedLocals.insert({ PD, it->second });
 366
 367       auto copyIt = LocalDeclMap.find(VD);
 368       assert(copyIt != LocalDeclMap.end() && "parameter copy is not found");
 369       it->second = copyIt->getSecond();
 370     }
 371
 372     ~ParamReferenceReplacerRAII() {
 373       for (auto&& SavedLocal : SavedLocals) {
 374         LocalDeclMap.insert({SavedLocal.first, SavedLocal.second});
 375       }
 376     }
 377   };
 378 }
 379
 380 // For WinEH exception representation backend needs to know what funclet coro.end
 381 // belongs to. That information is passed in a funclet bundle.
 382 static SmallVector<llvm::OperandBundleDef, 1>
 383 getBundlesForCoroEnd(CodeGenFunction &CGF) {
 384   SmallVector<llvm::OperandBundleDef, 1> BundleList;
 385
 386   if (llvm::Instruction *EHPad = CGF.CurrentFuncletPad)
 387     BundleList.emplace_back("funclet", EHPad);
 388
 389   return BundleList;
 390 }
 391
 392 namespace {
 393 // We will insert coro.end to cut any of the destructors for objects that
 394 // do not need to be destroyed once the coroutine is resumed.
 395 // See llvm/docs/Coroutines.rst for more details about coro.end.
 396 struct CallCoroEnd final : public EHScopeStack::Cleanup {
 397   void Emit(CodeGenFunction &CGF, Flags flags) override {
 398     auto &CGM = CGF.CGM;
 399     auto *NullPtr = llvm::ConstantPointerNull::get(CGF.Int8PtrTy);
 400     llvm::Function *CoroEndFn = CGM.getIntrinsic(llvm::Intrinsic::coro_end);
 401     // See if we have a funclet bundle to associate coro.end with. (WinEH)
 402     auto Bundles = getBundlesForCoroEnd(CGF);
 403     auto *CoroEnd = CGF.Builder.CreateCall(
 404         CoroEndFn, {NullPtr, CGF.Builder.getTrue()}, Bundles);
 405     if (Bundles.empty()) {
 406       // Otherwise, (landingpad model), create a conditional branch that leads
 407       // either to a cleanup block or a block with EH resume instruction.
 408       auto *ResumeBB = CGF.getEHResumeBlock(/*isCleanup=*/true);
 409       auto *CleanupContBB = CGF.createBasicBlock("cleanup.cont");
 410       CGF.Builder.CreateCondBr(CoroEnd, ResumeBB, CleanupContBB);
 411       CGF.EmitBlock(CleanupContBB);
 412     }
 413   }
 414 };
 415 }
 416
 417 namespace {
 418 // Make sure to call coro.delete on scope exit.
 419 struct CallCoroDelete final : public EHScopeStack::Cleanup {
 420   Stmt *Deallocate;
 421
 422   // Emit "if (coro.free(CoroId, CoroBegin)) Deallocate;"
 423
 424   // Note: That deallocation will be emitted twice: once for a normal exit and
 425   // once for exceptional exit. This usage is safe because Deallocate does not
 426   // contain any declarations. The SubStmtBuilder::makeNewAndDeleteExpr()
 427   // builds a single call to a deallocation function which is safe to emit
 428   // multiple times.
 429   void Emit(CodeGenFunction &CGF, Flags) override {
 430     // Remember the current point, as we are going to emit deallocation code
 431     // first to get to coro.free instruction that is an argument to a delete
 432     // call.
 433     BasicBlock *SaveInsertBlock = CGF.Builder.GetInsertBlock();
 434
 435     auto *FreeBB = CGF.createBasicBlock("coro.free");
 436     CGF.EmitBlock(FreeBB);
 437     CGF.EmitStmt(Deallocate);
 438
 439     auto *AfterFreeBB = CGF.createBasicBlock("after.coro.free");
 440     CGF.EmitBlock(AfterFreeBB);
 441
 442     // We should have captured coro.free from the emission of deallocate.
 443     auto *CoroFree = CGF.CurCoro.Data->LastCoroFree;
 444     if (!CoroFree) {
 445       CGF.CGM.Error(Deallocate->getBeginLoc(),
 446                     "Deallocation expressoin does not refer to coro.free");
 447       return;
 448     }
 449
 450     // Get back to the block we were originally and move coro.free there.
 451     auto *InsertPt = SaveInsertBlock->getTerminator();
 452     CoroFree->moveBefore(InsertPt);
 453     CGF.Builder.SetInsertPoint(InsertPt);
 454
 455     // Add if (auto *mem = coro.free) Deallocate;
 456     auto *NullPtr = llvm::ConstantPointerNull::get(CGF.Int8PtrTy);
 457     auto *Cond = CGF.Builder.CreateICmpNE(CoroFree, NullPtr);
 458     CGF.Builder.CreateCondBr(Cond, FreeBB, AfterFreeBB);
 459
 460     // No longer need old terminator.
 461     InsertPt->eraseFromParent();
 462     CGF.Builder.SetInsertPoint(AfterFreeBB);
 463   }
 464   explicit CallCoroDelete(Stmt *DeallocStmt) : Deallocate(DeallocStmt) {}
 465 };
 466 }
 467
 468 static void emitBodyAndFallthrough(CodeGenFunction &CGF,
 469                                    const CoroutineBodyStmt &S, Stmt *Body) {
 470   CGF.EmitStmt(Body);
 471   const bool CanFallthrough = CGF.Builder.GetInsertBlock();
 472   if (CanFallthrough)
 473     if (Stmt *OnFallthrough = S.getFallthroughHandler())
 474       CGF.EmitStmt(OnFallthrough);
 475 }
 476
 477 void CodeGenFunction::EmitCoroutineBody(const CoroutineBodyStmt &S) {
 478   auto *NullPtr = llvm::ConstantPointerNull::get(Builder.getInt8PtrTy());
 479   auto &TI = CGM.getContext().getTargetInfo();
 480   unsigned NewAlign = TI.getNewAlign() / TI.getCharWidth();
 481
 482   auto *EntryBB = Builder.GetInsertBlock();
 483   auto *AllocBB = createBasicBlock("coro.alloc");
 484   auto *InitBB = createBasicBlock("coro.init");
 485   auto *FinalBB = createBasicBlock("coro.final");
 486   auto *RetBB = createBasicBlock("coro.ret");
 487
 488   auto *CoroId = Builder.CreateCall(
 489       CGM.getIntrinsic(llvm::Intrinsic::coro_id),
 490       {Builder.getInt32(NewAlign), NullPtr, NullPtr, NullPtr});
 491   createCoroData(*this, CurCoro, CoroId);
 492   CurCoro.Data->SuspendBB = RetBB;
 493   assert(ShouldEmitLifetimeMarkers &&
 494          "Must emit lifetime intrinsics for coroutines");
 495
 496   // Backend is allowed to elide memory allocations, to help it, emit
 497   // auto mem = coro.alloc() ? 0 : ... allocation code ...;
 498   auto *CoroAlloc = Builder.CreateCall(
 499       CGM.getIntrinsic(llvm::Intrinsic::coro_alloc), {CoroId});
 500
 501   Builder.CreateCondBr(CoroAlloc, AllocBB, InitBB);
 502
 503   EmitBlock(AllocBB);
 504   auto *AllocateCall = EmitScalarExpr(S.getAllocate());
 505   auto *AllocOrInvokeContBB = Builder.GetInsertBlock();
 506
 507   // Handle allocation failure if 'ReturnStmtOnAllocFailure' was provided.
 508   if (auto *RetOnAllocFailure = S.getReturnStmtOnAllocFailure()) {
 509     auto *RetOnFailureBB = createBasicBlock("coro.ret.on.failure");
 510
 511     // See if allocation was successful.
 512     auto *NullPtr = llvm::ConstantPointerNull::get(Int8PtrTy);
 513     auto *Cond = Builder.CreateICmpNE(AllocateCall, NullPtr);
 514     Builder.CreateCondBr(Cond, InitBB, RetOnFailureBB);
 515
 516     // If not, return OnAllocFailure object.
 517     EmitBlock(RetOnFailureBB);
 518     EmitStmt(RetOnAllocFailure);
 519   }
 520   else {
 521     Builder.CreateBr(InitBB);
 522   }
 523
 524   EmitBlock(InitBB);
 525
 526   // Pass the result of the allocation to coro.begin.
 527   auto *Phi = Builder.CreatePHI(VoidPtrTy, 2);
 528   Phi->addIncoming(NullPtr, EntryBB);
 529   Phi->addIncoming(AllocateCall, AllocOrInvokeContBB);
 530   auto *CoroBegin = Builder.CreateCall(
 531       CGM.getIntrinsic(llvm::Intrinsic::coro_begin), {CoroId, Phi});
 532   CurCoro.Data->CoroBegin = CoroBegin;
 533
 534   CurCoro.Data->CleanupJD = getJumpDestInCurrentScope(RetBB);
 535   {
 536     CGDebugInfo *DI = getDebugInfo();
 537     ParamReferenceReplacerRAII ParamReplacer(LocalDeclMap);
 538     CodeGenFunction::RunCleanupsScope ResumeScope(*this);
 539     EHStack.pushCleanup<CallCoroDelete>(NormalAndEHCleanup, S.getDeallocate());
 540
 541     // Create mapping between parameters and copy-params for coroutine function.
 542     llvm::ArrayRef<const Stmt *> ParamMoves = S.getParamMoves();
 543     assert(
 544         (ParamMoves.size() == 0 || (ParamMoves.size() == FnArgs.size())) &&
 545         "ParamMoves and FnArgs should be the same size for coroutine function");
 546     if (ParamMoves.size() == FnArgs.size() && DI)
 547       for (const auto Pair : llvm::zip(FnArgs, ParamMoves))
 548         DI->getCoroutineParameterMappings().insert(
 549             {std::get<0>(Pair), std::get<1>(Pair)});
 550
 551     // Create parameter copies. We do it before creating a promise, since an
 552     // evolution of coroutine TS may allow promise constructor to observe
 553     // parameter copies.
 554     for (auto *PM : S.getParamMoves()) {
 555       EmitStmt(PM);
 556       ParamReplacer.addCopy(cast<DeclStmt>(PM));
 557       // TODO: if(CoroParam(...)) need to surround ctor and dtor
 558       // for the copy, so that llvm can elide it if the copy is
 559       // not needed.
 560     }
 561
 562     EmitStmt(S.getPromiseDeclStmt());
 563
 564     Address PromiseAddr = GetAddrOfLocalVar(S.getPromiseDecl());
 565     auto *PromiseAddrVoidPtr =
 566         new llvm::BitCastInst(PromiseAddr.getPointer(), VoidPtrTy, "", CoroId);
 567     // Update CoroId to refer to the promise. We could not do it earlier because
 568     // promise local variable was not emitted yet.
 569     CoroId->setArgOperand(1, PromiseAddrVoidPtr);
 570
 571     // ReturnValue should be valid as long as the coroutine's return type
 572     // is not void. The assertion could help us to reduce the check later.
 573     assert(ReturnValue.isValid() == (bool)S.getReturnStmt());
 574     // Now we have the promise, initialize the GRO.
 575     // We need to emit `get_return_object` first. According to:
 576     // [dcl.fct.def.coroutine]p7
 577     // The call to get_return_object is sequenced before the call to
 578     // initial_suspend and is invoked at most once.
 579     //
 580     // So we couldn't emit return value when we emit return statment,
 581     // otherwise the call to get_return_object wouldn't be in front
 582     // of initial_suspend.
 583     if (ReturnValue.isValid()) {
 584       EmitAnyExprToMem(S.getReturnValue(), ReturnValue,
 585                        S.getReturnValue()->getType().getQualifiers(),
 586                        /*IsInit*/ true);
 587     }
 588
 589     EHStack.pushCleanup<CallCoroEnd>(EHCleanup);
 590
 591     CurCoro.Data->CurrentAwaitKind = AwaitKind::Init;
 592     CurCoro.Data->ExceptionHandler = S.getExceptionHandler();
 593     EmitStmt(S.getInitSuspendStmt());
 594     CurCoro.Data->FinalJD = getJumpDestInCurrentScope(FinalBB);
 595
 596     CurCoro.Data->CurrentAwaitKind = AwaitKind::Normal;
 597
 598     if (CurCoro.Data->ExceptionHandler) {
 599       // If we generated IR to record whether an exception was thrown from
 600       // 'await_resume', then use that IR to determine whether the coroutine
 601       // body should be skipped.
 602       // If we didn't generate the IR (perhaps because 'await_resume' was marked
 603       // as 'noexcept'), then we skip this check.
 604       BasicBlock *ContBB = nullptr;
 605       if (CurCoro.Data->ResumeEHVar) {
 606         BasicBlock *BodyBB = createBasicBlock("coro.resumed.body");
 607         ContBB = createBasicBlock("coro.resumed.cont");
 608         Value *SkipBody = Builder.CreateFlagLoad(CurCoro.Data->ResumeEHVar,
 609                                                  "coro.resumed.eh");
 610         Builder.CreateCondBr(SkipBody, ContBB, BodyBB);
 611         EmitBlock(BodyBB);
 612       }
 613
 614       auto Loc = S.getBeginLoc();
 615       CXXCatchStmt Catch(Loc, /*exDecl=*/nullptr,
 616                          CurCoro.Data->ExceptionHandler);
 617       auto *TryStmt =
 618           CXXTryStmt::Create(getContext(), Loc, S.getBody(), &Catch);
 619
 620       EnterCXXTryStmt(*TryStmt);
 621       emitBodyAndFallthrough(*this, S, TryStmt->getTryBlock());
 622       ExitCXXTryStmt(*TryStmt);
 623
 624       if (ContBB)
 625         EmitBlock(ContBB);
 626     }
 627     else {
 628       emitBodyAndFallthrough(*this, S, S.getBody());
 629     }
 630
 631     // See if we need to generate final suspend.
 632     const bool CanFallthrough = Builder.GetInsertBlock();
 633     const bool HasCoreturns = CurCoro.Data->CoreturnCount > 0;
 634     if (CanFallthrough || HasCoreturns) {
 635       EmitBlock(FinalBB);
 636       CurCoro.Data->CurrentAwaitKind = AwaitKind::Final;
 637       EmitStmt(S.getFinalSuspendStmt());
 638     } else {
 639       // We don't need FinalBB. Emit it to make sure the block is deleted.
 640       EmitBlock(FinalBB, /*IsFinished=*/true);
 641     }
 642   }
 643
 644   EmitBlock(RetBB);
 645   // Emit coro.end before getReturnStmt (and parameter destructors), since
 646   // resume and destroy parts of the coroutine should not include them.
 647   llvm::Function *CoroEnd = CGM.getIntrinsic(llvm::Intrinsic::coro_end);
 648   Builder.CreateCall(CoroEnd, {NullPtr, Builder.getFalse()});
 649
 650   if (Stmt *Ret = S.getReturnStmt()) {
 651     // Since we already emitted the return value above, so we shouldn't
 652     // emit it again here.
 653     cast<ReturnStmt>(Ret)->setRetValue(nullptr);
 654     EmitStmt(Ret);
 655   }
 656
 657   // LLVM require the frontend to mark the coroutine.
 658   CurFn->setPresplitCoroutine();
 659 }
 660
 661 // Emit coroutine intrinsic and patch up arguments of the token type.
 662 RValue CodeGenFunction::EmitCoroutineIntrinsic(const CallExpr *E,
 663                                                unsigned int IID) {
 664   SmallVector<llvm::Value *, 8> Args;
 665   switch (IID) {
 666   default:
 667     break;
 668   // The coro.frame builtin is replaced with an SSA value of the coro.begin
 669   // intrinsic.
 670   case llvm::Intrinsic::coro_frame: {
 671     if (CurCoro.Data && CurCoro.Data->CoroBegin) {
 672       return RValue::get(CurCoro.Data->CoroBegin);
 673     }
 674     CGM.Error(E->getBeginLoc(), "this builtin expect that __builtin_coro_begin "
 675                                 "has been used earlier in this function");
 676     auto *NullPtr = llvm::ConstantPointerNull::get(Builder.getInt8PtrTy());
 677     return RValue::get(NullPtr);
 678   }
 679   case llvm::Intrinsic::coro_size: {
 680     auto &Context = getContext();
 681     CanQualType SizeTy = Context.getSizeType();
 682     llvm::IntegerType *T = Builder.getIntNTy(Context.getTypeSize(SizeTy));
 683     llvm::Function *F = CGM.getIntrinsic(llvm::Intrinsic::coro_size, T);
 684     return RValue::get(Builder.CreateCall(F));
 685   }
 686   case llvm::Intrinsic::coro_align: {
 687     auto &Context = getContext();
 688     CanQualType SizeTy = Context.getSizeType();
 689     llvm::IntegerType *T = Builder.getIntNTy(Context.getTypeSize(SizeTy));
 690     llvm::Function *F = CGM.getIntrinsic(llvm::Intrinsic::coro_align, T);
 691     return RValue::get(Builder.CreateCall(F));
 692   }
 693   // The following three intrinsics take a token parameter referring to a token
 694   // returned by earlier call to @llvm.coro.id. Since we cannot represent it in
 695   // builtins, we patch it up here.
 696   case llvm::Intrinsic::coro_alloc:
 697   case llvm::Intrinsic::coro_begin:
 698   case llvm::Intrinsic::coro_free: {
 699     if (CurCoro.Data && CurCoro.Data->CoroId) {
 700       Args.push_back(CurCoro.Data->CoroId);
 701       break;
 702     }
 703     CGM.Error(E->getBeginLoc(), "this builtin expect that __builtin_coro_id has"
 704                                 " been used earlier in this function");
 705     // Fallthrough to the next case to add TokenNone as the first argument.
 706     [[fallthrough]];
 707   }
 708   // @llvm.coro.suspend takes a token parameter. Add token 'none' as the first
 709   // argument.
 710   case llvm::Intrinsic::coro_suspend:
 711     Args.push_back(llvm::ConstantTokenNone::get(getLLVMContext()));
 712     break;
 713   }
 714   for (const Expr *Arg : E->arguments())
 715     Args.push_back(EmitScalarExpr(Arg));
 716
 717   llvm::Function *F = CGM.getIntrinsic(IID);
 718   llvm::CallInst *Call = Builder.CreateCall(F, Args);
 719
 720   // Note: The following code is to enable to emit coro.id and coro.begin by
 721   // hand to experiment with coroutines in C.
 722   // If we see @llvm.coro.id remember it in the CoroData. We will update
 723   // coro.alloc, coro.begin and coro.free intrinsics to refer to it.
 724   if (IID == llvm::Intrinsic::coro_id) {
 725     createCoroData(*this, CurCoro, Call, E);
 726   }
 727   else if (IID == llvm::Intrinsic::coro_begin) {
 728     if (CurCoro.Data)
 729       CurCoro.Data->CoroBegin = Call;
 730   }
 731   else if (IID == llvm::Intrinsic::coro_free) {
 732     // Remember the last coro_free as we need it to build the conditional
 733     // deletion of the coroutine frame.
 734     if (CurCoro.Data)
 735       CurCoro.Data->LastCoroFree = Call;
 736   }
 737   return RValue::get(Call);
 738 }